I was greatly involved with the "Prairie Trains" through most of their existance. 44-tonner Visalia Electric 502 was by far the most commonly used, although the ex-Navy MRS-1 was the primary engine the last few years (having been acquired specifically for this use). 70-tonner Central California Traction 30 was used occasionally and F7 WP 917 was used a couple of times. As far as I know (I wasn't always there), the GP7 (SN 712) was not used on the train, due to Museum management concerns about track damage. (However, I was present for a "secret" trip with the 917 and 712 lashed-up together, and they didn't hurt the track a bit!)
The train usually consisted of the 653, "Circumnavigator's Club," the two SP coaches and the WP baggage car (which had a snack bar/souvenir stand inside, and a diesel generator to run the train's lights and fans--before we got the baggage car, an arc welder in a boxcar supplied "head-end power"). For several years, UP and WP cabooses were available for charter by groups and were often added to the train. Passengers paid an extra fare to ride in the Pullmans, which included lounge service by uniformed waiters.
All the above were very popular with the public, and provided a lot of revenue and publicity for the museum. Unfortunately, the train haters in charge of the place saw fit to drive away most of the people interested in working on that operation and gave away a lot of the equipment that they felt threatened by. Then they told people that the "Prairie Trains" were discontinued because "nobody wanted to work on them."